1. Field of the Invention.
The present invention relates to paper-making machines, and, more particularly, to edge detectors for guiding a continuous belt therein.
2. Description of the Related Art.
Prior paper-making machines include continuous belts such as those made of "forming fabric" or felt to conduct the paper web throughout the paper-making machine. These continuous belts run at high velocities and sometimes have a tendency to move transversely relative to the running direction of the belt, thereby causing the edge of the belt to roll up against, contact, and/or wear on an interior edge of the machine.
Prior sensing devices to monitor such undesirable motion include the use of a mechanical sensing device in the form of a steel paddle that is oriented along the side of the continuous belt, such that when the continuous belt rubs against the steel paddle, a signal is provided to a guide device indicative of the transverse position of the continuous belt. The guide device shifts or moves the continuous belt transversely back into its normal running position within the machine in a continuous manner. Normally such mechanisms include a guide roll to direct the continuous belt or forming fabric. A problem with such steel paddles is that the physical contact of rubbing with the high velocity moving belt causes grooves to form in the paddle over time, thereby inducing inaccuracies in the mechanical sensing device and wearing out the paddle. Additionally, the edges of the continuous belt may wear and fray with such contact.
Another type of edge sensing mechanism is that of an optical sensor. This type of sensor utilizes an optical pickup for determining the path or the location of the edge of the belt such that when the edge of the belt is in an undesirable location, a guide device is activated to move the continuous belt transversely back to its normal running position. A problem with optical sensors is that the optical pickup eyes must be clean to operate consistently. The paper-making environment normally has a large amount of particulate matter and fiber adjacent to optical edge sensors which tend to cause these optical sensors to signal falsely or not operate at all. Because of this problem, mechanical sensing devices are still used as a backup sensing mechanism. Additionally, such optical sensors are expensive.
What is needed in the art is a relatively inexpensive edge detector system able to withstand the paper-making environment.